Accompanied with downsizing of apparatuses in which a semiconductor device is built, downsizing and thinning of a wiring substrate, which is included in the semiconductor device and generally made of resin, has been requested. However, thinning of the wiring substrate reduces the rigidity thereof.
In such a case, an LSI (semiconductor chip) is connected to a wiring substrate having a larger coefficient of linear expansion compared with the LSI, by means of reflow soldering using solder balls, then a thermal stress caused by the difference in the coefficient of linear expansion between the LSI and the wiring substrate affects the cooling process after the reflow, so that the LSI tends to warp and have a protruded shape. As a result, insufficient connection at a solder-connection part may occur. In addition, when a heat sink is provided on the upper surface of the LSI, heat radiation performance may be reduced due to a warp of the LSI.
In order to solve the above problem, Patent Document 1 discloses a structure in which an LSI is connected to a main surface (corresponding to the first surface of the present invention) of a wiring substrate by means of flip-chip connection, and a plate material (as a reinforcing member), which has a coefficient of linear expansion smaller than that of the wiring substrate and close to that of the LSI, and is made of alumina ceramics or zirconia, is adhered to a back surface (corresponding to the second surface of the present invention) of the wiring substrate, which is opposite to the main surface.
According to the above structure, since the wiring substrate is interposed between the plate member and the LSI which has a smaller coefficient of linear expansion than that of the substrate, a force which causes a warp of the wiring substrate is reduced so that the warp of the wiring substrate can be almost completely suppressed.
In a semiconductor device disclosed in Patent Document 2, a support plate is adhered to a first main surface (corresponding to the second surface of the present invention) of an organic wiring substrate (corresponding to the wiring substrate of the present invention), and a semiconductor chip is connected to a second main surface (corresponding to the first surface of the present invention) of the organic wiring substrate, which is opposite to the first main surface.
As the support plate, a metal plate (as a reinforcing member) made of copper or tungsten copper is used, which has a coefficient of linear expansion close to that of the semiconductor chip. On a surface of the support plate opposite to the surface to which the organic wiring substrate is adhered, a thin layer part and a rib frame structure are provided. The rib frame structure is a beam frame structure which crosses the thin layer part in the longitudinal and transverse directions no as to support the thin layer part. The semiconductor device having such a structure improves heat radiation performance and reduces the degree of a warp by increasing the surface area of the support plate by using the rib frame structure.
In a semiconductor module (i.e., semiconductor device) disclosed in Patent Document 3, a metal circuit plate (as a semiconductor chip) is formed on one surface (corresponding to the first surface of the present invention) of a ceramic substrate (corresponding to the wiring substrate of the present invention), and a heat radiating metal plate thicker than the metal circuit plate is formed on the other surface (corresponding to the second surface of the present invention) of the ceramic substrate. The heat radiating metal plate has slits in the thickness direction.
According to such a structure of the semiconductor module, it is possible to improve the heat radiation efficiency and durability.